Composites of stretch broken aligned fibers of carbon and glass reinforced resin

ABSTRACT

A coating of a viscous lubricant applied prior to stretch-breaking permits forming slivers of stretch-broken carbon fibers. When an anti-static ingredient is added to the viscous lubricant cohesive slivers of stretch-broken glass fibers can be formed. Composites of matrix resin reinforced with these slivers exhibit high strength, tensile stiffness, and good formability.

This is a division of application Ser. No. 942,441, filed Dec. 16, 1986,now U.S. Pat. No. 4,759,985.

BACKGROUND OF THE INVENTION

This invention relates to a process for stretch breaking carbon andglass filaments and using the stretch broken slivers therefrom to form acomposite of either a matrix reinforced with carbon fibers or a matrixreinforced with glass fibers.

Composite sheets of either continuous filament carbon fiber reinforcedresin or continuous filament glass fiber reinforced resin have beenmade. One technique is to prepare a warp of filaments as by winding on aframe, impregnating them with resins and hot pressing to form a thinflat sheet which is cut from the frame. Several such sheets are thencross lapped and again hot pressed to form the final reinforcedcomposite product. Such products have high strength and stiffness.

Problems occur when attempts are made to produce deep drawn threedimensional articles by hot pressing continuous carbon or glass filamentcontaining resin sheets. The articles in many instances exhibit unevenareas and wrinkles. The use of staple carbon or glass fibers asreinforcement substantially overcomes the above-stated problems but at agreat sacrifice to strength and stiffness.

In a similar situation involving P-aramid fibers, a solution to theaforementioned problem was the use of certain stretch broken P-aramidfibers as disclosed by Fish and Lauterbach in U.S. Pat. No. 4,552,805.However, because carbon and glass filaments exhibit little or nocohesive capability when processed according to known stretch-breakingprocesses, slivers of carbon or glass fibers have not been able to beformed by these known processes.

The present invention permits forming cohesive slivers of stretch brokenfilaments of carbon and glass for use in forming a composite carbon orglass fiber reinforced resin useful for deep drawing purposes withlittle sacrifice of strength and stiffness.

SUMMARY OF THE INVENTION

A cohesive sliver of stretch broken glass or carbon fibers having a highdegree of axial alignment and a coating of a finish comprising a viscouslubricant and an anti-static ingredient. Composites of a matrix resinreinforced with such slivers and shaped structures formed therefrom arealso encompassed.

BRIEF DESCRIPTIONN OF THE DRAWING

FIG. 1 is a schematic illustration of a preferred embodiment apparatusfor use with a continuous process in the practice of the presentinvention.

FIG. 2 is a schematic illustration of apparatus for applying finish to acarbon or glass filament yarn.

FIG. 3 is a schematic illustration of apparatus for stretch-breaking acohesive carbon or glass yarn.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, the preferred embodiment generally includes a creel10 for yarn supply packages 12, a plurality of yarn tensioning barsgenerally designated 14, a finish applicator 16 comprised of a rotatablefinish roll 18 emersed in a pan 20 filled with a liquid finish 22 a pairof grooved roller guides 24,26 are located between the finish applicator16 and a Turbo Stapler 28 (manufactured by the Turbo Machine Co.,Lansdale, Pa.). The Turbo-Stapler includes a pair of driven nip rolls30,32 which firmly grip the tow band 34 that has been consolidated fromthe individual yarns in guide 29. The nip rolls 30,32 feed tow band 34at a constant rate to a pair of front rolls 36,38 which also grip thetow band 34 and withdraw it from breaker bars 39 and feed it as a sliverto a condensing guide 40 from which the sliver is fed to a windup (notshown) for packaging.

In operation, glass or carbon yarn 13 from individual packages 12 is fedfrom creel 10 over finish roll 18 where it is coated with finish 22. Theyarns are consolidated in guide 29, tensioned between rolls 30,32 andfront rolls 36,38, then randomly broken by sharply deflecting themlaterally by the breaker bars 39. The coating of finish on the yarn inthe sliver is sufficient to enable the sliver to be pulled through guide40 to the windup without disassociation of the fibers in the sliver.

While the continuous process illustrated in FIG. 1 is preferred, theapplication of finish to continuous filament carbon or glass fibers andthe stretch-breaking of the coated filaments can be carried out in twosteps; i.e., separate finish application and stretch-breaking processes,according to FIGS. 2 and 3 and as described subsequently in Example 1.More particularly, in FIG. 2, glass or carbon yarn 13 from package 12 isfed over yarn tensioning bar 14' over finish roll 18 where it is coatedwith finish 22 and wound onto a bobbin 12' and allowed to dry. The yarnfrom bobbins 12' is then stretch-broken by breaker bars 39 (FIG. 3) inthe turbo-stapler as described above in connection with FIG. 1.

The finish used in this invention is a material that causes aninterfilament viscous drag sufficiently high to permit the handlingrequired to make a composite, such as winding and unwinding from apackage. More particularly, the finish used for the carbon fiberapplication is a mixture of a one part of a suitable antistat and twoparts of a non-tacky viscous lubricant of a consistency to impart to thechopped sliver adequate cohesiveness (minimum of 0.01 gram per denier)without tackiness or without compromising the fiber-matrix adhesion inthe final composite. The antistat portion of the mixture could bereduced or even eliminated if the reinforcing fiber is electricallyconductive (e.g., carbon fibers).

A suitable viscous lubricant is polyethylene glycol (400 mol. wt)monolaurate and a lauric amide while a suitable antistat is mixed monoand di-phosphate esters of C8-C12 fatty alcohols neutralized withdiethanol amine.

Preferably, the percent finish on fiber is in the range of from about0.3% to about 0.5%.

Formable planar and shaped non-planar composites are contemplated by thepresent invention. For the formable composites, that is, thosecomposites that can be formed into shaped non-planar three-dimensionalstructures at elevated temperatures (where necessary), matrix resins ofthe thermoplastic variety or of the not fully cured thermoset type maybe employed. In the latter case the thermosettable resin is cured afterthe composite has been shaped. Suitable thermoplastic resins includepolyesters (including copolyesters), e.g., polyethylene terephthalate,Kodar® PETG copolyester 6763 (Eastman Kodak); polyamides, e.g., nylon6,6; polyolefins, e.g., polypropylene; also included are the hightemperature resins such as an amorphous polyamide copolymer based uponbis(para-aminocyclohexyl) methane, a semi-crystalline polyamidehomopolymer also based on bis(para-aminocyclohexyl) methane, andpolyetheretherketone. Thermosetting resins that are useful includephenolic resins, epoxy resin and vinyl ester resins.

The ratio of reinforcement to matrix can vary, but preferably is between40% to 75% by volume. The average fiber lengths also may vary butpreferably range from about 1/2 to about 6 inches in length with arandom overlap distribution. About 85 percent of the fibers are alignedwithin ±10 degrees, preferably ±5 degrees of the axial direction.

The composite may be made by a variety of procedures. Thus, a stretchbroken sliver may be wound on a frame covered with a film ofthermoplastic resin to form a warp. The warp of stretch-broken sliver,however, can be made by any technique known to those skilled in the art,e.g., by creeling or beaming. A preform is obtained when another film ofthermoplastic resin is placed over the warp to form a sandwich which isheated in a vacuum bag and then removed from the frame. Several of suchpreforms may be stacked while offset to provide multi-directionality andthen the stack may be heated under pressure to form a compositestructure.

Other techniques for applying matrix polymer include sprinkling ofpowdered resin on the sliver warp followed by heating to melt the resin,flowing liquid resin over the sliver warp, intermingling thermoplasticfiber with the sliver warp and then heating to melt the thermoplasticfiber thereby forming the matrix resin, calendering the warp betweenlayers of matrix film, etc.

TEST PROCEDURES Composite Tensile

The composite tensile tests followed the general procedure described inASTM Test D 3039-76 entitled "Standard Test Method for TensileProperties of Fiber--Resin Composites."

Short Beam Shear

The short beam shear tests followed the general procedure described inASTM Method D 2344-76 entitled, "Standard Test Method for ApparentInterlaminar Shear Strength of Parallel Fiber Composites by Short BeamMethod" with the following exception, the loading nose was 1/16 inchradius instead of 1/8 inch.

Sliver Cohesion

The yarn to be treated for sliver cohesion was placed in the clamps ofan Instron tensile testing machine set to a gauge length of 17 inches, acrosshead speed of 10 inches per minute and a chart speed of 12 inchesper minute. The crosshead was started to apply tension to the sample andthe maximum force in grams indicated on the chart was recorded anddivided by the sliver denier to give the sliver cohesion.

Finish on Yarn

Finish on yarn is determined in a method wherein weighed specimens areextracted gravimetrically with prescribed solvent(s) at roomtemperature, the solvent containing dissolved finish and any othermaterials which may wash off the specimens, is transferred to apreweighed container and evaporated. The extractable residue is weighed.Percentage extractables based on extractable-free specimen weight iscalculated. Aerothane® (1,1,1-trichloroethane) is used as the solventfor all finish materials except glycerine and methanol is used as thesolvent for that material.

High Temperature Tensile Drawing

The sample to be tested was placed in the clamps of an Instron tensiletesting machine set to a particular gauge length and a crosshead speeddepending on the sample. A thermocouple was attached the surface of thesample midway between the clamps and an 8 inch long electrically heatedcylindrical oven was placed around the sample leaving a one inch spacebetween the bottom of the oven and the lower clamp. The open ends of theoven were plugged with insulation material to prevent convective heatloss and heating of the clamps. The oven was turned on and the sampleheated to reduce its viscosity to permit drawing (temperature determinedby the viscosity, time, temperature data of the matrix material. Samplesmade with thermosetting matrix resins must be tested in their uncuredstate.). The sample was held at this temperature for 15 minutes toinsure thermal equilibrium. The crosshead was then started and allowedto run until the heated section of the sample was drawn 50%. The ovenwas removed and the sample inspected to determine whether it had broken.

Fiber Orientation

A photomicrograph of the surface of the composite (enlarged 240×) wasprepared. The angle between each fiber axis and the axial direction ofthe composite was measured with a protractor on the photomicrograph andtabulated. The percentage of fibers with an angle within ±5 degrees ofthe axial direction was reported.

EXAMPLE 1

Four bobbins of 2000 denier continuous filament carbon fiber (3K AS-4from Hercules Inc.) were prepared for stretch-breaking by applying afinish composed of two parts of a lubricant (polyethylene glycolmonolaurate and a lauric amide) and one part of an antistat (mixed monoand diphosphate esters of C8-C12 fatty alcohols neutralized withdiethanol amine). The finish was applied by running the continuousfilament carbon fiber, one bobbin at a time, at 75 yards/minute over afinish roll which was wet with a 4% aqueous emulsion of thelubricant-antistat mixture (FIG. 2). The four bobbins were allowed tostand overnight to evaporate the water. Finish level after drying was0.33%.

The four bobbins of carbon fiber were stretch-broken on a Turbo-stapler(Turbo Machine Co., Lansdale, PA) as shown in FIG. 3. The surface speedof the rolls (30,32) was 35.4 yards/minute and the surface speed of thefront rolls (36,38) was 110 yards/minute. The tip speed of the breakerbars (39) was 71 yards/minute. The resulting sliver as 2422 denier andhad a cohesion value of 0.18 grams/denier which was sufficient to allowwinding without twist on a cylindrical paper tube using a Leesona type959 winder. The average fiber length of fifty measurements of thissliver was 3.2 inches (shortest 0.7 inch, longest 5.6 inches).

A warp was prepared from this sliver by winding it from the paper tube,25 ends to the inch on a 16 inch square metal plate. A 2.0 mil thickfilm of thermoplastic resin (an amorphous polyamide copolymer based onbis(para-aminocyclohexyl)methane) was placed on the frame before windingthe sliver and another was added after winding was complete. The entiresandwich was vacuum bagged at 280° C. for 15 minutes after which time itwas cut from the plate. This product, called a preform was now awell-impregnated, relatively stiff matrix/stretch-broken sliversandwich, in which all the slivers were aligned in one direction.

Twelve of these preforms were stacked on top of one another with all thefibers in the same direction. This stack was heated in a mold at 305° C.at 500 pounds per square inch for 35 minutes to make a well-consolidatedplate 93 mils thick and fiber volume fraction of 55%. Short beam sheartests conducted on 0.5 inch wide strips cut from this plate gave a valueof 13,700 pounds per square inch. It was concluded that the presence ofthe finish did not adversely affect the adhesion of the fiber to thematrix polymer.

A second plate was made from ten of these preforms by stacking them sothat the direction of the stretch-broken fibers were offset by 45degrees in a clockwide direction in successive layers. The bottom planeof the fifth layer was considered a reflecting plane and the next fivelayers were stacked so that the warp directions of the stretch-brokensliver were mirror images of the top five layers with respect to thatplane. This sandwich was molded as above to make a well consolidatedplate with a fiber volume fraction of 55%. This plate was heated to 322°C. and molded into a hemisphere with a radius of 3 inches. The plateconformed very well to the shape of the mold and it was concluded thatthe product was deep drawable without wrinkles.

EXAMPLE 2

A sliver of stretch-broken glass fiber was prepared by the method inExample 1 except that 6700 denier continuous filament glass fiber wasused (T-30 P353B from Owens-Corning Fiberglass) and the finish wasapplied by spraying a 10% aqueous emulsion on the fiber. The emulsionwas pumped to the spray nozzle at 5 cc. per minute and the air pressureused was 3 psi. The yarn was pulled past the spray head at 55 yards perminute by a pair of nip rolls and wound on a cylindrical paper tube.After drying, the finish level was 0.35%. Stretch-broken sliver wasprepared from two finish treated continuous filament bobbins and had acohesion of 0.09 grams per denier which was adequate for winding as inExample 1. Further, the finish controlled static generation in thestretch-breaking process to an acceptable level. The average fiberlength of fifty measurements of this sliver was 3.4 inches (shortest 1.0inch, longest 10.2 inches).

A unidirectional plate was made from this sliver and PETG film (Kodar®PETG copolyester 6763, Eastman Kodak) by the method of Example 1 exceptthat the sliver spacing was 26 ends per inch, the film thickness was 3.0mils and 8 layers of preform were used to 55% fiber volume fraction.Short beam shear tests on 0.5 inch wide strips cut from this plate gavea result of 5,400 pounds per square inch. It was concluded that thepresence of the finish did not affect the adhesion of the fiber to thematrix polymer.

EXAMPLE 3

A sample of carbon fiber sliver was prepared using the stretch-breakingprocess of Example 1 except that finish was not pre-applied to thecontinuous fiber and two bobbins were used instead of four. The two endsof carbon fiber were contacted by a felt pad saturated with glycerinewhich was placed between the tension guide and the infeed roll.Glycerine level on the sliver was 0.5%. The average fiber length offifty measurements of this sliver was 3.2 inches (shortest 0.6 inch,longest 7.9 inch). Cohesion was measured as a function of time vs. thesliver from Example 1 with the following results.

    ______________________________________                                                  Cohesion, grams per denier                                          Days        Glycerine  Example 1                                              ______________________________________                                        1           .58        .15                                                    9           .79        .24                                                    16          .02        .25                                                    22          .02        .25                                                    30          .02        .21                                                    ______________________________________                                    

EXAMPLE 4

Glycerine treated sliver from Example 3 was made into a warp, preformsand a unidirectional plate by the method of Example 1. The end count was12 per inch, the film was 3.0 mol thick PETG (Kodar® PETG copolyester6763 from Eastman Kodak) and 6 preforms were stacked to make the platewhich was 40% fiber volume fraction. The plate was cut into 0.5 inchstrips, provided with aluminum tabs and subjected to tensile tests at 8inch guage length with the following results:

    ______________________________________                                        Tensile strength, psi.                                                                              127,400                                                 Modulus, psi.         11,600,000                                              ______________________________________                                    

It was concluded that the product had very high strength and modulus.The uniformity of orientation of the fibers on the surface of this platewere measured from a photomicrograph and it was found that 85% of thefibers were within ±5 degrees of the axial direction.

EXAMPLE 5

Continuous filament 2000 denier carbon fiber was made into a warp,preforms and a unidirectional plate. The end count was 12 per inch, thefilm was 3.0 mil thick PETG (Kodar® PETG copolyester 6763 from EastmanKodak) and 16 preforms were stacked to make the plate which was 40%fiber volume fraction. The plate was cut into 0.5 inch strips, providedwith aluminum tabs and subjected to tensile tests at 8 inch guage lengthwith the following results:

    ______________________________________                                        Tensile strength, psi.                                                                              139,800                                                 Modulus, psi.         11,600,000                                              ______________________________________                                    

It was concluded that the product of Example 4 exhibited the strengthand stiffness expected of continuous filament carbon fiber. The productof Example 4, although made of stretch-broken discontinuous staplefiber, came within 90% of the strength and stiffness of the continuousfilament product. This excellent performance is believed due to the highdegree of order of the stretch-broken fibers.

EXAMPLE 6

Stretch broken glass sliver was prepared by the method of Example 2except that finish was not pre-applied to the continuous fiber. Instead,the fiber being supplied to the Turbo-stapler was sprayed periodicallywith Jif-Job antistatic spray (Schafco, Lancaster, PA). The roll andbreaker bar speeds were one-half the values in Example 2. The averagefiber length of fifty measurements of this sliver was 3.1 inches(shortest 1.0 inch, longest 5.8 inch). This sliver was made into a warp,preforms and a unidirectional plate by the method of Example 1. The endcount was 21 per inch, the film was 3.0 mil thick PETG (Kodar® PETGcopolyester 6763 from Eastman Kodak) and 5 preforms were stacked to makethe plate which was 40% fiber volume fraction. The plate was cut into0.5 inch strips, provided with aluminum tabs and subjected to tensiletests at 8 inch gauge length with the following results:

    ______________________________________                                        Tensile strength, psi. 67,200                                                 Modulus, psi.          4,950,000                                              ______________________________________                                    

It was concluded that the product had very high strength and modulus.

EXAMPLE 7 Continuous filament 6700 denier glass fiber was made into awarp, preforms and a unidirectional plate. The end count was 13 perinch, the film was 3.0 mils thick PETG (Kodar® PETG copolyester 6763from Eastman Kodak) and 5 preforms were stacked to make the plate whichwas 40% fiber volume fraction. The plate was cut into 0.5 inch strips,provided with aluminum tabs and subjected to tensile tests at 8 inchguage length with the following results:

    ______________________________________                                        Tensile strength, psi. 67,900                                                 Modulus, psi.          5,460,000                                              ______________________________________                                    

It was concluded that the product of Example 6 exhibited the strengthand stiffness expected of continuous filament glass fiber. The productof Example 6, although made of discontinuous staple fiber, came within90% of the strength and stiffness of the continuous filament product.

EXAMPLE 8

A preform of stretch broken carbon fiber sliver in an epoxy resin(Hercules 3501-6) was made by the following procedure:

(1) The frozen resin was thawed at room temperature, then heated to 180°F. for 15 minutes.

(2) A film of resin was cast onto release paper then chilled to 40° F.to stop the polymerization reaction and the exposed surface was coveredwith polyester film for protection.

(3) The paper-resin-film sandwich was wound on a 7-foot diameter drumand the polyester film removed.

(4) 2300 denier graphite sliver made by the process of Example 1 waswound on the exposed resin at 9 ends per inch for a total width of 10.5inches. The average fiber length of fifty measurements of this sliverwas 3.2 inches (shortest 0.7 inch, longest 5.6 inches).

(5) The polyester film was removed from a second paper-resin-filmsandwich and wound over the graphite layer on the drum to make apaper-resin-graphite-resin-paper sandwich.

(6) The sandwich was unwound from the drum and vacuum bagged flat at140° F. for 10 minutes to force the resin into the graphite layer, thenfrozen for later use. The thickness of the resin-graphite part of thissandwich was 7 mils.

A unidirectional composite strip made by stacking together ten layers of3/4-inch wide and 14-inch long strips (fiber direction parallel to the14-inch dimension) of the graphite-resin preform was vacuum bagged fortwo minutes. One inch on either end of the strip was partially cured byheating it to 120° C. for two hours while keeping the middle 12 inchesof the strip cold with dry ice. At a guage length of 11 inches and acrosshead speed of 5 inches per minute, a high temperature tensiledrawing test was conducted at 124° C. on the 14 inch long by 0.75 inchwide strip which showed the composite could be drawn 50% withoutbreaking, predicting a high degree of formability.

A composite plate was made from 10 layers of the sandwich from step 6above by removing the release paper, cutting the graphite-resin preforminto sheets and stacking them so that the direction of thestretch-broken fibers were offset by 45 degrees in a clockwise directionin successive layers. The bottom plane of the fifth layer was considereda reflecting plane and the next five layers were stacked so that thewarp directions of the stretch-broken sliver were mirror images of thetop five layers with respect to that plane. This sandwich wasvacuum-bagged at ambient temperature for 2 minutes to stick the layerstogether. This plate was molded into a hemisphere with a radius of 3inches and cured in the mold at 175° C. for 2 hours. The plate conformedvery well to the shape of the mold and it was concluded that the productwas formable.

EXAMPLE 9

Four bobbins of 2000 denier continuous filament carbon fiber (3K AS-4from Hercules Inc.) were stretch-broken on a Turbo-stapler (TurboMachine Co., Lansdale, PA) set up as shown in FIG. 1. A 10% aqueoussolution of the finish described in Example 1 was applied with a wettedroll. The surface speed of the intermediate rolls was 17.7 yards/minuteand the surface speed of the front rolls was 55 yards/minute. The tipspeed of the breaker bars was 35.5 yards/minute. The resulting sliverwas 2250 denier. The average fiber length of fifty measurements of thissliver was 3.3 inches (shortest 0.8inch, longest 5.5 inches).

A warp was prepared from this sliver by winding it, 27 ends to the inchon a 18 inch square metal plate. A 3.0 mil thick film of thermoplasticresin (PETG copolyester) was placed on the frame before winding thesliver and another was added after winding was complete. The entiresandwich was vacuum bagged at 220° C. for 15 minutes after which time itwas cut from the frame. This product, called a preform was now awell-impregnated, relatively stiff matrix/stretch-broken sliversandwich, in which all the slivers were aligned in one direction.

Seven of these preforms were stacked on top of one another with all thefibers in the same direction. This stack was heated in a mold at 200° C.at 400 pounds per square inch for 30 minutes to make a well-consolidatedplate 82 mils thick and fiber volume fraction of 50%. High temperaturetensile drawing tests at a guage length of 10 inches and crosshead speedof 10 inches per minute conducted at 262° C. on 12 inch long by 0.75inch wide strips cut from this plate with the fiber direction parallelto the 12 inch dimension showed the composite could be drawn 50% withoutbreaking, predicting a high degree of formability.

EXAMPLE 10

Two bobbins of 6700 denier continuous filament glass fiber (T-30 P353Bfrom Owens-Corning Fiberglass) were stretch-broken on a Turbo-stapler(Turbo Machine Co., Lansdale, PA) set up as shown in FIG. 1. A 10%aqueous solution of the finish described in Example 1 was aplied with awetted roll. The surface speed of the intermediate rolls was 17.7yards/minute and the surface speed of the front rolls was 55yards/minute. The tip speed of the breaker bars was 35.5 yards/minute.The resulting sliver was 4100 denier. The average fiber length of fiftymeasurements of this sliver was 3.4 inches (shortest 0.9 inch, longest8.7 inches).

A warp was prepared from this sliver by winding it, 22 ends to the inchon a 18 inch square metal plate. A 3.0 mil thick film of thermoplasticresin (PETG copolyester) was placed on the frame before winding thesliver and another was added after winding was complete. The entiresandwich was vacuum bagged at 220° C. for 15 minutes after which time itwas cut from the frame. This product, called a preform was now awell-impregnated, relatively stiff matrix/stretch-broken sliversandwich, in which all the slivers were aligned in one direction.

Seven of these preforms were stacked on top of one another with all thefibers in the same direction. This stack was heated in a mold at 200° C.at 400 pounds per square inch for 30 minutes to make a well-consolidatedplate 82 mils thick and fiber volume fraction of 50%. High temperaturetensile drawing tests at a gauge length of 10 inches and crosshead speedof 10 inches per minute conducted at 262° C. on 12 inch long by 0.75inch wide strips cut from this plate with the fiber direction parallelto the 12 inch dimension showed the composite could be drawn 50% withoutbreaking, predicting a high degree of formability.

EXAMPLE 11

Sliver from Example 10 was re-broken to reduce the fiber length bypassing it through two sets of elastomer coated nip rolls with aseparation of 2.50 inches between the nips. The surface speed of thesecond set of rolls was 10 yards per minute and the surface speed of thefirst set of rolls was 7.1 yards per minute giving a draft of 1.4.Denier of this re-broken sliver was 5371 and the average fiber length offifty measurements of this silver was 1.57 inches (shortest 0.5 inch,longest 3.6 inches).

A `warp` was prepared from this sliver by winding it, 17 ends to theinch on a 18 inch square metal plate. A 3.0 mil thick film ofthermoplastic resin (PETG copolyester) was placed on the frame beforewinding the sliver and another was added after winding was complete. Theentire sandwich was vacuum bagged at 220° C. for 15 minutes after whichtime it was cut from the frame. This product, called a preform was now awell-impregnated, relatively stiff matrix/stretch-broken sliversandwich, in which all the slivers were aligned in one direction.

Seven of these preforms were stacked on top of one another with all thefibers in the same direction. This stack was heated in a mold at 200° C.at 400 pounds per square inch for 30 minutes to make a well-consolidatedplate 80 mils thick and fiber volume fraction of 50%. High temperaturetensile drawing tests at a guage length of 10 inches and crosshead speedof 10 inches per minute conducted at 262° C. on 12 inch long by 0.75inch wide strip cut from this plate with the fiber direction parallel tothe 12 inch dimension showed the composite could be drawn 50% withoutbreaking, predicting a high degree of formability.

EXAMPLE 12

Sliver from Example 9 was re-broken to reduce the fiber length bypassing it through two sets of elastomer coated nip rolls with aseparation of 2.50 inches between the nips. The surface speed of thesecond set of rolls was 10 yards per minute and the surface speed of thefirst set of roll was 7.1 yards per minute giving a draft of 1.4. Denierof this re-broken sliver was 4623 and the average fiber length of fiftymeasurements of this sliver was 1.33 inches (shortest 0.6 inch, longest3.1 inches).

A warp was prepared from this sliver by winding it, 13 ends to the inchon an 18 inch square metal plate. A 3.0 mil thick film of thermoplasticresin (PETG copolyester) was placed on the frame before winding thesliver and another was added after winding was complete. The entiresandwich was vacuum bagged at 220° C. for 15 minutes after which time itwas cut from the frame. This product, called a preform was now awell-impregnated, relatively stiff matrix/stretch-broken sliversandwich, in which all the slivers were aligned in one direction.

Seven of these preforms were stacked on top of one another with all thefibers in the same direction. This stack was heated in a mold at 200° C.at 400 pounds per square inch for 30 minutes to make a well-consolidatedplate 80 mils thick and fiber volume fraction of 50%. High temperaturetensile drawing tests, at a guage length of 10 inches and a crossheadspeed of 10 inches per minute, conducted, at 262° C., on 12 inch long by0.75 inch wide strips cut from this plate with the fiber directionparallel to the 12 inch dimension showed the composite could be drawn50% without breaking, predicting a high degree of formability.

EXAMPLE 13

A pre-laminate was prepared from glass fiber from Example 2 by acontinuous process as follows: 46 ends of sliver were fed from a creelinto a 6 inch wide warp which was sandwiched between two 1.0 ml PETpoly(ethylene terephthalate) film to give a pre-laminate of 55% fibervolume fraction. A release film of `Kapton` polyimide was placed on eachside of this sandwich to prevent sticking of molten PET to hot surfaces.This sandwich was then passed at 10 feet per minute through the nip oftwo steel rolls heated to 278° C. to tack the assembly together.

A composite plate was made from this pre-laminate by removing therelease film, trimming the excess PET from the edges and placing stripsof pre-laminate in layers in a 16 inch square mold. Each layer was madeup of side-by side strips of pre-laminate to reach the required 16 inchwidth.

A plate was made from 10 layers of pre-laminate by arranging them sothat the direction of the stretch-broken fibers were offset by 45degrees in a clockwise direction in successive layers. The bottom planeof the fifth layer was considered a reflecting plane and the next fivelayers were stacked so that the warp directions of the stretch-brokensliver were mirror images of the top five layers with respect to thatplane. This sandwich was molded as in Example 2 to make awell-consolidated composite plate with a fiber volume fraction of 55%.This plate was heated to 280° C. and molded into a hemisphere with aradius of 3 inches. The plate conformed very well to the shape of themold and it was concluded that the product was formable.

EXAMPLE 14

A plate was made from 10 layers of pre-forms made by the method ofExample 11 by arranging them in a 16 inch square mold so that thedirection of the stretch-broken fibers were offset by 45 degrees in aclockwise direction in successive layers. The bottom plane of the fifthlayer was considered a reflecting plane and the next five layers werestacked so that the warp directions of the stretch-broken sliver weremirror images of the top five layers with respect to that plane. Thissandwich was molded as in Example 2 to make a well-consolidatedcomposite plate with a fiber volume fraction of 55%. This plate washeated to 280° C. and molded into a hemisphere with a radius of 3inches. The plate conformed very well to the shape of the mold and itwas concluded that the product was formable.

EXAMPLE 15

Continuous filament 2000 denier carbon fiber was made into a warp,preforms and a unidirectional plate by the method of Example 1. The endcount was 25 per inch, the film was 2.0 mil thick film of thermoplasticresin (an amorphous polyamide copolymer based onbis(para-aminocyclohexyl)methane). Seven preforms were stacked to makethe plate which was 55 mils thick and 55% fiber volume fraction. Theplate was cut into 0.5 inch strips, provided with aluminum tabs andsubjected to tensile tests at 8 inch gauge length with the followingresults:

    ______________________________________                                        Tensile strength, psi.                                                                              243,200                                                 Modulus, psi.         18,200,000                                              ______________________________________                                    

It was concluded that the product had very high strength and modulus.

EXAMPLE 16

A warp was prepared from sliver from example 9 by winding it, 21 ends tothe inch on a 18 inch square metal plate. A 2.0 mil thick film ofthermoplastic resin (an amorphous polyamide copolymer based onbis(para-aminocyclohexl)methane) was placed on the frame before windingthe sliver and another was added after winding was complete. The entiresandwich was vacuum bagged at 280° C. for 20 minutes after which time itwas cut from the frame. This product, called a preform was now awell-impregnated, relatively stiff matrix/stretch-broken sliversandwich, in which all the slivers were aligned in one direction.

Seven of these preforms were stacked on top of one another with all thefibers in the same direction. This stack was heated in a mold to 305° C.at 600 pounds per square inch for 40 minutes to make a well-consolidatedplate 58 mils thick and fiber volume fraction of 55%. One half inchstrips cut from this plate were subjected to tensile tests at 8 inchgauge length with the following results:

    ______________________________________                                        Tensile strength, psi 246,000                                                 Modulus, psi          18,800,000                                              ______________________________________                                    

The uniformity of orientation of the fibers on the surface of this platewere measured from a photomicrograph and it was found that 92% of thefibers were within ±5 degrees of the axial direction. The product ofthis example, although made of discontinuous staple fiber, wasequivalent to the strength and modulus of continuous filament fiber(Example 15).

EXAMPLE 17

Continuous filament 6700 denier glass fiber was made into a warp,preforms and a unidirectional plate by the method of Example 1. The endcount was 15.5 per inch, the film was 3.0 mol thick PET(poly(ethyleneterephthalate)) and 5 preforms were stacked to make theplate which was 55% fiber volume fraction. The plate was cut into 0.5inch strips, provided with aluminum tabs and subjected to tensile testsat 8 inch gauge length with the following results:

    ______________________________________                                        Tensile strength, psi. 156,000                                                Modulus, psi.          7,300,000                                              ______________________________________                                    

It was concluded that the product of Example 17 exhibited the strengthand stiffness expected of continuous filament glass fiber.

EXAMPLE 18

A unidirectional plate was made from pre-laminate from Example 13 bystacking 5 layers in a mold with all slivers in the same direction andheating in a press as in the reference example to give a final thicknessof 103 mils. One-half inch strips cut from this plate were subjected totensile tests at 8 inch gauge length with the following results:

    ______________________________________                                        Tensile Strength, psi  86,800                                                 Modulus, psi           5,900,000                                              ______________________________________                                    

It was concluded that strength and modulus of the product of thisexample, although not as high as those from continuous filament glass(Example 17) were far superior to those of randomly oriented glasscomposites of equivalent fiber volume fraction reported in theliterature (ref. B. D. Agarwal, L. J. Broutman, "Analysis andPerformance of Fiber Composites" p. 92) which are:

    ______________________________________                                        Tensile Strength, psi  23,000                                                 Modulus, psi           2,400,000                                              ______________________________________                                    

We claim:
 1. A composite comprising a layer of a matrix resin reinforcedwith a sliver of substantially axially aligned stretch broken glassstaple fibers having an average length greater than 0.50 inches and acohesion of at least 0.01 grams/denier, said fibers having a coatingfinish thereon comprising a viscous lubricant and an antistaticingredient.
 2. The composite of claim 1 wherein about 85% of the fibersare aligned within ±10 degrees of the axial direction.
 3. The compositeof claims 1 or 2 wherein said fibers have an average length in the rangeof from about 1/2 to about 6 inches.
 4. The composite of claims 1 or 2said composite having a high temperature tensile elongation of up toabout 50 percent without breaking.
 5. The composite of claims 1 or 2wherein the fiber comprises between 40% to about 75% by volume of thecomposite.
 6. The composite as in any one of claims 1 or 2 in which thematrix is a thermoplastic resin.
 7. The composite as in any one ofclaims 1 or 2 in which the matrix is a thermosetting resin.
 8. Thecomposite as in any one of claims 1 or 2 in which the matrix is an epoxyresin.
 9. The composite of claim 1, there being a plurality of layerswherein some of the layers are offset with respect to each other.